This paper presents a hydrologic modeling application to assess climate change impacts on the water resources of the Rio Conchos basin, especially for agriculture and domestic water uses. The study basin is located in the Mexican State of Chihuahua, with a drainage area around 67,862 km2. It is one of the most important Mexican tributaries of the binational Rio Grande basin and contributes major water deliveries (about 55) to US through the 1944 treaty between Mexico and the US. However, during period of drought, for instance in the 1990s, there has been conflict and competition for the water resources in the basin, and as a consequence Mexico accumulated an important water debt to the US. In addition, the hydrological behavior of the basin has recurrent periods of water stress, problems with long drought periods, allocation and release, and water pollution. Under this reality, it is important to evaluate and predict the available water resources in the next 50 or 100 years taking account of possible climate change impacts in the basin as well as assessing the policies to be implemented in order to face drought periods and preserve the agreements treaty between Mexico and the US. For this purpose, the Water Evaluation and Planning (WEAP) model is used. The model was calibrated and validated comparing the simulated flows resulting from the input of climatic time series with naturalized flows. Monthly climate time series from 1980-1999 (20 years) were used and some soil parameters were adjusted for calibration. Also, comparisons between simulated and naturalized flows were performed for different stations. In addition to this, calibration considering all water management infrastructures, such as, reservoirs, operation rules, canals, and diversions, was also carried out. The results show good correlation between simulated and observed flows which indicates that the model reproduces the hydrologic behavior of the basin, including, natural and historical flows, storage in reservoirs, water supplies, and water demands for agriculture and urban activities. © 2009 ASCE.